The present invention relates to an apparatus for monitoring air pressure of automobile tires. More particularly, the present invention pertains to a transmitter and method for transmitting information regarding tire air pressure to a receiver mounted on a vehicle body.
Wireless tire air pressure monitoring apparatuses for allowing a driver in a vehicle passenger compartment to check the pressure of vehicle tires have been proposed. One such monitoring system includes transmitters and a receiver. Each transmitter is located in one of the wheels and the receiver is located in the body frame of the vehicle. Each transmitter detects the pressure of the associated tire and wirelessly transmits the detection information. The receiver receives information from the transmitters.
Since each transmitter is powered by a battery, the transmitter stops operating when the battery runs down. Each transmitter is attached to the corresponding wheel and is located in the corresponding tire. To change the battery of a transmitter, the tire must be removed from the wheel. Changing the battery of a transmitter is therefore burdensome. Further, the transmitters are constructed with a high accuracy to be durable against the harsh condition in the tire. Therefore, opening the casing of a transmitter for changing the battery can make the transmitter less reliable. Accordingly, changing the battery is not practical.
The capacity of the battery may be increased to permit the transmitter to function for a long period without changing the battery. This, however, increases the size and the weight of the battery thus altering the balance of the corresponding tire. Therefore, the capacity of the battery cannot be increased beyond a certain limit.
To extend the life of the batteries, some prior art apparatuses use transmitters that only periodically transmit signals. This minimizes the cumulative operating time of the transmitters, which allows batteries having a relatively small capacity to be used for a long period.
Tire pressure can change at various rates. For example, natural leakage of air gradually decreases the pressure of a tire. When a tire goes flat due to damage, the air pressure drops quickly. Further, the rates of pressure loss from natural leakage and the damage vary according to the circumstances. Thus, there is a demand for an air monitoring apparatus that immediately detects rapid air pressure changes and extends battery life.
However, simply making transmissions from a transmitter periodic cannot satisfy this need. As long as the tire pressure decreases slowly, relatively long transmission intervals cause no problem in detecting an abnormality. However, if the tire pressure suddenly decreases, the driver will not be immediately informed of abnormality. If the transmission intervals are relatively short, the driver will be immediately notified of a sudden drop in tire pressure. However, the short intervals increase the cumulative operating time of the transmitter, which shortens the life of the battery.
Accordingly, it is an objective of the present invention to provide a transmitter in a tire air monitoring apparatus and a method that immediately inform a driver of air pressure abnormality and conserve battery strength.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a battery-powered transmitter for wirelessly transmitting data regarding the inner pressure of a vehicle tire is provided. The transmitter includes a pressure sensor for measuring the inner pressure of the tire, a transmission circuit for wirelessly transmitting data representing the measured tire pressure and a controller for controlling the transmission circuit to periodically transmit the data at predetermined transmission intervals. When the tire pressure changes by an amount that is equal to or greater than a predetermined upper limit value during a predetermined judging time, the controller controls the transmission circuit to transmit the data earlier than the next data transmission that would take place according to the periodic transmission intervals.
In another aspect of the present invention, a method for wirelessly transmitting data regarding the inner pressure of a vehicle tire by a battery-powered transmitter, is provided. The method includes measuring the inner pressure of the tire, periodically and wirelessly transmitting data representing the measured tire pressure at regular transmission intervals and performing an early wireless transmission, which occur before the next data transmission would take place according to the regular transmission intervals, when the tire pressure changes by an amount that is equal to or greater than a predetermined upper limit value during a predetermined judging time.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.